From 6d1c46746e17367caf8a24623cb5c9a9c4e3e036 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@redhat.com>
Date: Mon, 20 May 2019 11:02:00 +0200
Subject: [PATCH] bpo-36763: Fix Python preinitialization (GH-13432)

* Add _PyPreConfig.parse_argv
* Add _PyCoreConfig._config_init field and _PyCoreConfigInitEnum enum
  type
* Initialization functions: reject preconfig=NULL and config=NULL
* Add config parameter to _PyCoreConfig_DecodeLocaleErr(): pass
  config->argv to _Py_PreInitializeFromPyArgv(), to parse config
  command line arguments in preinitialization.
* Add config parameter to _PyCoreConfig_SetString(). It now
  preinitializes Python.
* _PyCoreConfig_SetPyArgv() now also preinitializes Python for wide
  argv
* Fix _Py_PreInitializeFromCoreConfig(): don't pass args to
  _Py_PreInitializeFromPyArgv() if config.parse_argv=0.
* Use "char * const *" and "wchar_t * const *" types for 'argv'
  parameters and _PyArgv.argv.
* Add unit test on preinitialization from argv.
* _PyPreConfig.allocator type becomes int
* Add _PyPreConfig_InitFromPreConfig() and
  _PyPreConfig_InitFromCoreConfig() helper functions
---
 Include/cpython/coreconfig.h         |  22 ++-
 Include/cpython/pylifecycle.h        |   4 +-
 Include/internal/pycore_coreconfig.h |  10 +-
 Lib/test/test_embed.py               |  96 +++++++---
 Programs/_testembed.c                | 264 ++++++++++++++++++++++-----
 Python/coreconfig.c                  | 123 +++++++------
 Python/preconfig.c                   |  80 +++++---
 Python/pylifecycle.c                 |  57 ++++--
 8 files changed, 477 insertions(+), 179 deletions(-)

diff --git a/Include/cpython/coreconfig.h b/Include/cpython/coreconfig.h
index a71f16171b7..decfb70e734 100644
--- a/Include/cpython/coreconfig.h
+++ b/Include/cpython/coreconfig.h
@@ -44,6 +44,10 @@ typedef struct {
     int _config_version;  /* Internal configuration version,
                              used for ABI compatibility */
 
+    /* Parse _Py_PreInitializeFromArgs() arguments?
+       See _PyCoreConfig.parse_argv */
+    int parse_argv;
+
     /* If greater than 0, enable isolated mode: sys.path contains
        neither the script's directory nor the user's site-packages directory.
 
@@ -111,8 +115,9 @@ typedef struct {
 
     int dev_mode;           /* Development mode. PYTHONDEVMODE, -X dev */
 
-    /* Memory allocator: PYTHONMALLOC env var */
-    PyMemAllocatorName allocator;
+    /* Memory allocator: PYTHONMALLOC env var.
+       See PyMemAllocatorName for valid values. */
+    int allocator;
 } _PyPreConfig;
 
 PyAPI_FUNC(void) _PyPreConfig_InitPythonConfig(_PyPreConfig *config);
@@ -121,9 +126,16 @@ PyAPI_FUNC(void) _PyPreConfig_InitIsolatedConfig(_PyPreConfig *config);
 
 /* --- _PyCoreConfig ---------------------------------------------- */
 
+typedef enum {
+    _PyCoreConfig_INIT = 0,
+    _PyCoreConfig_INIT_PYTHON = 1,
+    _PyCoreConfig_INIT_ISOLATED = 2
+} _PyCoreConfigInitEnum;
+
 typedef struct {
     int _config_version;  /* Internal configuration version,
                              used for ABI compatibility */
+    int _config_init;     /* _PyCoreConfigInitEnum value */
 
     int isolated;         /* Isolated mode? see _PyPreConfig.isolated */
     int use_environment;  /* Use environment variables? see _PyPreConfig.use_environment */
@@ -401,19 +413,21 @@ PyAPI_FUNC(_PyInitError) _PyCoreConfig_InitPythonConfig(_PyCoreConfig *config);
 PyAPI_FUNC(_PyInitError) _PyCoreConfig_InitIsolatedConfig(_PyCoreConfig *config);
 PyAPI_FUNC(void) _PyCoreConfig_Clear(_PyCoreConfig *);
 PyAPI_FUNC(_PyInitError) _PyCoreConfig_SetString(
+    _PyCoreConfig *config,
     wchar_t **config_str,
     const wchar_t *str);
 PyAPI_FUNC(_PyInitError) _PyCoreConfig_DecodeLocale(
+    _PyCoreConfig *config,
     wchar_t **config_str,
     const char *str);
 PyAPI_FUNC(_PyInitError) _PyCoreConfig_Read(_PyCoreConfig *config);
 PyAPI_FUNC(_PyInitError) _PyCoreConfig_SetArgv(
     _PyCoreConfig *config,
     Py_ssize_t argc,
-    char **argv);
+    char * const *argv);
 PyAPI_FUNC(_PyInitError) _PyCoreConfig_SetWideArgv(_PyCoreConfig *config,
     Py_ssize_t argc,
-    wchar_t **argv);
+    wchar_t * const *argv);
 
 #ifdef __cplusplus
 }
diff --git a/Include/cpython/pylifecycle.h b/Include/cpython/pylifecycle.h
index 8fc809d30d8..1e1dabe59ff 100644
--- a/Include/cpython/pylifecycle.h
+++ b/Include/cpython/pylifecycle.h
@@ -35,11 +35,11 @@ PyAPI_FUNC(_PyInitError) _Py_InitializeFromConfig(
 PyAPI_FUNC(_PyInitError) _Py_InitializeFromArgs(
     const _PyCoreConfig *config,
     Py_ssize_t argc,
-    char **argv);
+    char * const *argv);
 PyAPI_FUNC(_PyInitError) _Py_InitializeFromWideArgs(
     const _PyCoreConfig *config,
     Py_ssize_t argc,
-    wchar_t **argv);
+    wchar_t * const *argv);
 PyAPI_FUNC(_PyInitError) _Py_InitializeMain(void);
 
 PyAPI_FUNC(int) _Py_RunMain(void);
diff --git a/Include/internal/pycore_coreconfig.h b/Include/internal/pycore_coreconfig.h
index edde7b1d8d8..324e0b82b90 100644
--- a/Include/internal/pycore_coreconfig.h
+++ b/Include/internal/pycore_coreconfig.h
@@ -63,8 +63,8 @@ PyAPI_FUNC(int) _PyWstrList_Extend(_PyWstrList *list,
 typedef struct {
     Py_ssize_t argc;
     int use_bytes_argv;
-    char **bytes_argv;
-    wchar_t **wchar_argv;
+    char * const *bytes_argv;
+    wchar_t * const *wchar_argv;
 } _PyArgv;
 
 PyAPI_FUNC(_PyInitError) _PyArgv_AsWstrList(const _PyArgv *args,
@@ -121,6 +121,12 @@ PyAPI_FUNC(_PyInitError) _PyPreCmdline_Read(_PyPreCmdline *cmdline,
 /* --- _PyPreConfig ----------------------------------------------- */
 
 PyAPI_FUNC(void) _PyPreConfig_Init(_PyPreConfig *config);
+PyAPI_FUNC(void) _PyPreConfig_InitFromCoreConfig(
+    _PyPreConfig *config,
+    const _PyCoreConfig *coreconfig);
+PyAPI_FUNC(void) _PyPreConfig_InitFromPreConfig(
+    _PyPreConfig *config,
+    const _PyPreConfig *config2);
 PyAPI_FUNC(void) _PyPreConfig_Copy(_PyPreConfig *config,
     const _PyPreConfig *config2);
 PyAPI_FUNC(PyObject*) _PyPreConfig_AsDict(const _PyPreConfig *config);
diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index 5a5419dcfcf..5be179a266b 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -17,6 +17,10 @@ PYMEM_ALLOCATOR_NOT_SET = 0
 PYMEM_ALLOCATOR_DEBUG = 2
 PYMEM_ALLOCATOR_MALLOC = 3
 
+CONFIG_INIT = 0
+CONFIG_INIT_PYTHON = 1
+CONFIG_INIT_ISOLATED = 2
+
 
 class EmbeddingTestsMixin:
     def setUp(self):
@@ -280,11 +284,19 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
 
     DEFAULT_PRE_CONFIG = {
         'allocator': PYMEM_ALLOCATOR_NOT_SET,
+        'parse_argv': 0,
         'configure_locale': 1,
         'coerce_c_locale': 0,
         'coerce_c_locale_warn': 0,
         'utf8_mode': 0,
     }
+    if MS_WINDOWS:
+        DEFAULT_PRE_CONFIG.update({
+            'legacy_windows_fs_encoding': 0,
+        })
+    PYTHON_PRE_CONFIG = dict(DEFAULT_PRE_CONFIG,
+        parse_argv=1,
+    )
     ISOLATED_PRE_CONFIG = dict(DEFAULT_PRE_CONFIG,
         configure_locale=0,
         isolated=1,
@@ -292,8 +304,6 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         utf8_mode=0,
         dev_mode=0,
     )
-    if MS_WINDOWS:
-        ISOLATED_PRE_CONFIG['legacy_windows_fs_encoding'] = 0
 
     COPY_PRE_CONFIG = [
         'dev_mode',
@@ -302,6 +312,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
     ]
 
     DEFAULT_CORE_CONFIG = {
+        '_config_init': CONFIG_INIT,
         'isolated': 0,
         'use_environment': 1,
         'dev_mode': 0,
@@ -365,9 +376,6 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         '_init_main': 1,
     }
     if MS_WINDOWS:
-        DEFAULT_PRE_CONFIG.update({
-            'legacy_windows_fs_encoding': 0,
-        })
         DEFAULT_CORE_CONFIG.update({
             'legacy_windows_stdio': 0,
         })
@@ -439,13 +447,14 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
 
     def get_expected_config(self, expected_preconfig, expected, env, api,
                             add_path=None):
-        if api == "python":
+        if api == CONFIG_INIT_PYTHON:
             default_config = self.PYTHON_CORE_CONFIG
-        elif api == "isolated":
+        elif api == CONFIG_INIT_ISOLATED:
             default_config = self.ISOLATED_CORE_CONFIG
         else:
             default_config = self.DEFAULT_CORE_CONFIG
         expected = dict(default_config, **expected)
+        expected['_config_init'] = api
 
         code = textwrap.dedent('''
             import json
@@ -519,9 +528,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         return expected
 
     def check_pre_config(self, config, expected):
-        pre_config = dict(config['pre_config'])
-        core_config = dict(config['core_config'])
-        self.assertEqual(pre_config, expected)
+        self.assertEqual(config['pre_config'], expected)
 
     def check_core_config(self, config, expected):
         core_config = dict(config['core_config'])
@@ -554,7 +561,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         self.assertEqual(config['global_config'], expected)
 
     def check_config(self, testname, expected_config=None, expected_preconfig=None,
-                     add_path=None, stderr=None, api="default"):
+                     add_path=None, stderr=None, api=CONFIG_INIT):
         env = dict(os.environ)
         # Remove PYTHON* environment variables to get deterministic environment
         for key in list(env):
@@ -565,8 +572,10 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         env['PYTHONCOERCECLOCALE'] = '0'
         env['PYTHONUTF8'] = '0'
 
-        if api == "isolated":
+        if api == CONFIG_INIT_ISOLATED:
             default_preconfig = self.ISOLATED_PRE_CONFIG
+        elif api == CONFIG_INIT_PYTHON:
+            default_preconfig = self.PYTHON_PRE_CONFIG
         else:
             default_preconfig = self.DEFAULT_PRE_CONFIG
         if expected_preconfig is None:
@@ -719,7 +728,38 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'dev_mode': 1,
             'warnoptions': ['default'],
         }
-        self.check_config("init_dev_mode", config, preconfig, api="python")
+        self.check_config("init_dev_mode", config, preconfig,
+                          api=CONFIG_INIT_PYTHON)
+
+    def test_preinit_parse_argv(self):
+        # Pre-initialize implicitly using argv: make sure that -X dev
+        # is used to configure the allocation in preinitialization
+        preconfig = {
+            'allocator': PYMEM_ALLOCATOR_DEBUG,
+        }
+        config = {
+            'argv': ['script.py'],
+            'run_filename': 'script.py',
+            'dev_mode': 1,
+            'faulthandler': 1,
+            'warnoptions': ['default'],
+            'xoptions': ['dev'],
+        }
+        self.check_config("preinit_parse_argv", config, preconfig,
+                          api=CONFIG_INIT_PYTHON)
+
+    def test_preinit_dont_parse_argv(self):
+        # -X dev must be ignored by isolated preconfiguration
+        preconfig = {
+            'isolated': 0,
+        }
+        config = {
+            'argv': ["python3", "-E", "-I",
+                     "-X", "dev", "-X", "utf8", "script.py"],
+            'isolated': 0,
+        }
+        self.check_config("preinit_dont_parse_argv", config, preconfig,
+                          api=CONFIG_INIT_ISOLATED)
 
     def test_init_isolated_flag(self):
         config = {
@@ -727,7 +767,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'use_environment': 0,
             'user_site_directory': 0,
         }
-        self.check_config("init_isolated_flag", config, api="python")
+        self.check_config("init_isolated_flag", config, api=CONFIG_INIT_PYTHON)
 
     def test_preinit_isolated1(self):
         # _PyPreConfig.isolated=1, _PyCoreConfig.isolated not set
@@ -747,25 +787,30 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         }
         self.check_config("preinit_isolated2", config)
 
+    def test_preinit_isolated_config(self):
+        self.check_config("preinit_isolated_config", api=CONFIG_INIT_ISOLATED)
+
     def test_init_isolated_config(self):
-        self.check_config("init_isolated_config", api="isolated")
+        self.check_config("init_isolated_config", api=CONFIG_INIT_ISOLATED)
 
     def test_init_python_config(self):
-        self.check_config("init_python_config", api="python")
+        self.check_config("init_python_config", api=CONFIG_INIT_PYTHON)
 
     def test_init_dont_configure_locale(self):
         # _PyPreConfig.configure_locale=0
         preconfig = {
             'configure_locale': 0,
         }
-        self.check_config("init_dont_configure_locale", {}, preconfig, api="python")
+        self.check_config("init_dont_configure_locale", {}, preconfig,
+                          api=CONFIG_INIT_PYTHON)
 
     def test_init_read_set(self):
         core_config = {
             'program_name': './init_read_set',
             'executable': 'my_executable',
         }
-        self.check_config("init_read_set", core_config, api="python",
+        self.check_config("init_read_set", core_config,
+                          api=CONFIG_INIT_PYTHON,
                           add_path="init_read_set_path")
 
     def test_init_run_main(self):
@@ -777,7 +822,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'run_command': code + '\n',
             'parse_argv': 1,
         }
-        self.check_config("init_run_main", core_config, api="python")
+        self.check_config("init_run_main", core_config,
+                          api=CONFIG_INIT_PYTHON)
 
     def test_init_main(self):
         code = ('import _testinternalcapi, json; '
@@ -789,7 +835,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'parse_argv': 1,
             '_init_main': 0,
         }
-        self.check_config("init_main", core_config, api="python",
+        self.check_config("init_main", core_config,
+                          api=CONFIG_INIT_PYTHON,
                           stderr="Run Python code before _Py_InitializeMain")
 
     def test_init_parse_argv(self):
@@ -800,15 +847,20 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'run_command': 'pass\n',
             'use_environment': 0,
         }
-        self.check_config("init_parse_argv", core_config, api="python")
+        self.check_config("init_parse_argv", core_config,
+                          api=CONFIG_INIT_PYTHON)
 
     def test_init_dont_parse_argv(self):
+        pre_config = {
+            'parse_argv': 0,
+        }
         core_config = {
             'parse_argv': 0,
             'argv': ['./argv0', '-E', '-c', 'pass', 'arg1', '-v', 'arg3'],
             'program_name': './argv0',
         }
-        self.check_config("init_dont_parse_argv", core_config, api="python")
+        self.check_config("init_dont_parse_argv", core_config, pre_config,
+                          api=CONFIG_INIT_PYTHON)
 
 
 if __name__ == "__main__":
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index f1bb731dcba..3dabf66de15 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -527,7 +527,10 @@ static int check_init_parse_argv(int parse_argv)
     _PyInitError err;
 
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
 
     static wchar_t* argv[] = {
         L"./argv0",
@@ -565,7 +568,7 @@ static int test_init_dont_parse_argv(void)
 }
 
 
-static void test_init_env_putenvs(void)
+static void set_all_env_vars(void)
 {
     putenv("PYTHONHASHSEED=42");
     putenv("PYTHONMALLOC=malloc");
@@ -596,7 +599,7 @@ static int test_init_env(void)
 {
     /* Test initialization from environment variables */
     Py_IgnoreEnvironmentFlag = 0;
-    test_init_env_putenvs();
+    set_all_env_vars();
     _testembed_Py_Initialize();
     dump_config();
     Py_Finalize();
@@ -604,9 +607,9 @@ static int test_init_env(void)
 }
 
 
-static void set_all_env_vars(void)
+static void set_all_env_vars_dev_mode(void)
 {
-    test_init_env_putenvs();
+    set_all_env_vars();
     putenv("PYTHONMALLOC=");
     putenv("PYTHONFAULTHANDLER=");
     putenv("PYTHONDEVMODE=1");
@@ -617,7 +620,7 @@ static int test_init_env_dev_mode(void)
 {
     /* Test initialization from environment variables */
     Py_IgnoreEnvironmentFlag = 0;
-    set_all_env_vars();
+    set_all_env_vars_dev_mode();
     _testembed_Py_Initialize();
     dump_config();
     Py_Finalize();
@@ -629,7 +632,7 @@ static int test_init_env_dev_mode_alloc(void)
 {
     /* Test initialization from environment variables */
     Py_IgnoreEnvironmentFlag = 0;
-    set_all_env_vars();
+    set_all_env_vars_dev_mode();
     putenv("PYTHONMALLOC=malloc");
     _testembed_Py_Initialize();
     dump_config();
@@ -644,7 +647,10 @@ static int test_init_isolated_flag(void)
 
     /* Test _PyCoreConfig.isolated=1 */
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
 
     Py_IsolatedFlag = 0;
     config.isolated = 1;
@@ -727,6 +733,107 @@ static int test_preinit_isolated2(void)
 }
 
 
+static int test_preinit_dont_parse_argv(void)
+{
+    _PyInitError err;
+
+    _PyPreConfig preconfig;
+    _PyPreConfig_InitIsolatedConfig(&preconfig);
+
+    preconfig.isolated = 0;
+
+    /* -X dev must be ignored by isolated preconfiguration */
+    wchar_t *argv[] = {L"python3",
+                       L"-E",
+                       L"-I",
+                       L"-X", L"dev",
+                       L"-X", L"utf8",
+                       L"script.py"};
+    err = _Py_PreInitializeFromWideArgs(&preconfig, Py_ARRAY_LENGTH(argv), argv);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    _PyCoreConfig config;
+
+    err = _PyCoreConfig_InitIsolatedConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    config.isolated = 0;
+
+    /* Pre-initialize implicitly using argv: make sure that -X dev
+       is used to configure the allocation in preinitialization */
+    err = _PyCoreConfig_SetWideArgv(&config, Py_ARRAY_LENGTH(argv), argv);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    err = _PyCoreConfig_SetString(&config, &config.program_name,
+                                  L"./_testembed");
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    err = _Py_InitializeFromConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+    _PyCoreConfig_Clear(&config);
+
+    dump_config();
+    Py_Finalize();
+    return 0;
+
+failed:
+    _PyCoreConfig_Clear(&config);
+    _Py_ExitInitError(err);
+}
+
+
+static int test_preinit_parse_argv(void)
+{
+    _PyInitError err;
+    _PyCoreConfig config;
+
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    /* Pre-initialize implicitly using argv: make sure that -X dev
+       is used to configure the allocation in preinitialization */
+    wchar_t *argv[] = {L"python3", L"-X", L"dev", L"script.py"};
+    err = _PyCoreConfig_SetWideArgv(&config, Py_ARRAY_LENGTH(argv), argv);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    err = _PyCoreConfig_SetString(&config, &config.program_name,
+                                  L"./_testembed");
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    err = _Py_InitializeFromConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+    _PyCoreConfig_Clear(&config);
+
+    dump_config();
+    Py_Finalize();
+    return 0;
+
+failed:
+    _PyCoreConfig_Clear(&config);
+    _Py_ExitInitError(err);
+}
+
+
+
+
 static void set_all_global_config_variables(void)
 {
     Py_IsolatedFlag = 0;
@@ -749,9 +856,10 @@ static void set_all_global_config_variables(void)
 }
 
 
-static int test_init_isolated_config(void)
+static int check_preinit_isolated_config(int preinit)
 {
     _PyInitError err;
+    _PyPreConfig *rt_preconfig;
 
     /* environment variables must be ignored */
     set_all_env_vars();
@@ -759,18 +867,20 @@ static int test_init_isolated_config(void)
     /* global configuration variables must be ignored */
     set_all_global_config_variables();
 
-    _PyPreConfig preconfig;
-    _PyPreConfig_InitIsolatedConfig(&preconfig);
+    if (preinit) {
+        _PyPreConfig preconfig;
+        _PyPreConfig_InitIsolatedConfig(&preconfig);
 
-    err = _Py_PreInitialize(&preconfig);
-    if (_PyInitError_Failed(err)) {
-        _Py_ExitInitError(err);
+        err = _Py_PreInitialize(&preconfig);
+        if (_PyInitError_Failed(err)) {
+            _Py_ExitInitError(err);
+        }
+
+        rt_preconfig = &_PyRuntime.preconfig;
+        assert(rt_preconfig->isolated == 1);
+        assert(rt_preconfig->use_environment == 0);
     }
 
-    _PyPreConfig *rt_preconfig = &_PyRuntime.preconfig;
-    assert(rt_preconfig->isolated == 1);
-    assert(rt_preconfig->use_environment == 0);
-
     _PyCoreConfig config;
     err = _PyCoreConfig_InitIsolatedConfig(&config);
     if (_PyInitError_Failed(err)) {
@@ -782,13 +892,30 @@ static int test_init_isolated_config(void)
     if (_PyInitError_Failed(err)) {
         _Py_ExitInitError(err);
     }
+
+    rt_preconfig = &_PyRuntime.preconfig;
+    assert(rt_preconfig->isolated == 1);
+    assert(rt_preconfig->use_environment == 0);
+
     dump_config();
     Py_Finalize();
     return 0;
 }
 
 
-static int test_init_python_config(void)
+static int test_preinit_isolated_config(void)
+{
+    return check_preinit_isolated_config(1);
+}
+
+
+static int test_init_isolated_config(void)
+{
+    return check_preinit_isolated_config(0);
+}
+
+
+static int check_init_python_config(int preinit)
 {
     _PyInitError err;
 
@@ -805,12 +932,14 @@ static int test_init_python_config(void)
     Py_LegacyWindowsStdioFlag = 1;
 #endif
 
-    _PyPreConfig preconfig;
-    _PyPreConfig_InitPythonConfig(&preconfig);
+    if (preinit) {
+        _PyPreConfig preconfig;
+        _PyPreConfig_InitPythonConfig(&preconfig);
 
-    err = _Py_PreInitialize(&preconfig);
-    if (_PyInitError_Failed(err)) {
-        _Py_ExitInitError(err);
+        err = _Py_PreInitialize(&preconfig);
+        if (_PyInitError_Failed(err)) {
+            _Py_ExitInitError(err);
+        }
     }
 
     _PyCoreConfig config;
@@ -830,6 +959,18 @@ static int test_init_python_config(void)
 }
 
 
+static int test_preinit_python_config(void)
+{
+    return check_init_python_config(1);
+}
+
+
+static int test_init_python_config(void)
+{
+    return check_init_python_config(0);
+}
+
+
 static int test_init_dont_configure_locale(void)
 {
     _PyInitError err;
@@ -846,7 +987,10 @@ static int test_init_dont_configure_locale(void)
     }
 
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
     config.program_name = L"./_testembed";
     err = _Py_InitializeFromConfig(&config);
     if (_PyInitError_Failed(err)) {
@@ -861,13 +1005,17 @@ static int test_init_dont_configure_locale(void)
 
 static int test_init_dev_mode(void)
 {
+    _PyInitError err;
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
     putenv("PYTHONFAULTHANDLER=");
     putenv("PYTHONMALLOC=");
     config.dev_mode = 1;
     config.program_name = L"./_testembed";
-    _PyInitError err = _Py_InitializeFromConfig(&config);
+    err = _Py_InitializeFromConfig(&config);
     if (_PyInitError_Failed(err)) {
         _Py_ExitInitError(err);
     }
@@ -881,9 +1029,13 @@ static int test_init_read_set(void)
 {
     _PyInitError err;
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
 
-    err = _PyCoreConfig_DecodeLocale(&config.program_name, "./init_read_set");
+    err = _PyCoreConfig_DecodeLocale(&config, &config.program_name,
+                                     "./init_read_set");
     if (_PyInitError_Failed(err)) {
         goto fail;
     }
@@ -900,7 +1052,7 @@ static int test_init_read_set(void)
     }
 
     /* override executable computed by _PyCoreConfig_Read() */
-    err = _PyCoreConfig_SetString(&config.executable, L"my_executable");
+    err = _PyCoreConfig_SetString(&config, &config.executable, L"my_executable");
     if (_PyInitError_Failed(err)) {
         goto fail;
     }
@@ -937,11 +1089,15 @@ static void configure_init_main(_PyCoreConfig *config)
 
 static int test_init_run_main(void)
 {
+    _PyInitError err;
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
     configure_init_main(&config);
 
-    _PyInitError err = _Py_InitializeFromConfig(&config);
+    err = _Py_InitializeFromConfig(&config);
     if (_PyInitError_Failed(err)) {
         _Py_ExitInitError(err);
     }
@@ -952,12 +1108,17 @@ static int test_init_run_main(void)
 
 static int test_init_main(void)
 {
+    _PyInitError err;
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        _Py_ExitInitError(err);
+    }
     configure_init_main(&config);
     config._init_main = 0;
 
-    _PyInitError err = _Py_InitializeFromConfig(&config);
+    err = _Py_InitializeFromConfig(&config);
     if (_PyInitError_Failed(err)) {
         _Py_ExitInitError(err);
     }
@@ -982,23 +1143,40 @@ static int test_init_main(void)
 
 static int test_run_main(void)
 {
+    _PyInitError err;
     _PyCoreConfig config;
-    _PyCoreConfig_InitPythonConfig(&config);
+
+    err = _PyCoreConfig_InitPythonConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
 
     wchar_t *argv[] = {L"python3", L"-c",
                        (L"import sys; "
                         L"print(f'_Py_RunMain(): sys.argv={sys.argv}')"),
                        L"arg2"};
-    config.argv.length = Py_ARRAY_LENGTH(argv);
-    config.argv.items = argv;
-    config.program_name = L"./python3";
-
-    _PyInitError err = _Py_InitializeFromConfig(&config);
+    err = _PyCoreConfig_SetWideArgv(&config, Py_ARRAY_LENGTH(argv), argv);
     if (_PyInitError_Failed(err)) {
-        _Py_ExitInitError(err);
+        goto failed;
     }
 
+    err = _PyCoreConfig_SetString(&config, &config.program_name,
+                                  L"./python3");
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+
+    err = _Py_InitializeFromConfig(&config);
+    if (_PyInitError_Failed(err)) {
+        goto failed;
+    }
+    _PyCoreConfig_Clear(&config);
+
     return _Py_RunMain();
+
+failed:
+    _PyCoreConfig_Clear(&config);
+    _Py_ExitInitError(err);
 }
 
 
@@ -1039,10 +1217,14 @@ static struct TestCase TestCases[] = {
     { "init_dont_configure_locale", test_init_dont_configure_locale },
     { "init_dev_mode", test_init_dev_mode },
     { "init_isolated_flag", test_init_isolated_flag },
+    { "preinit_isolated_config", test_preinit_isolated_config },
     { "init_isolated_config", test_init_isolated_config },
+    { "preinit_python_config", test_preinit_python_config },
     { "init_python_config", test_init_python_config },
     { "preinit_isolated1", test_preinit_isolated1 },
     { "preinit_isolated2", test_preinit_isolated2 },
+    { "preinit_parse_argv", test_preinit_parse_argv },
+    { "preinit_dont_parse_argv", test_preinit_dont_parse_argv },
     { "init_read_set", test_init_read_set },
     { "init_run_main", test_init_run_main },
     { "init_main", test_init_main },
diff --git a/Python/coreconfig.c b/Python/coreconfig.c
index 470bda87028..958845e488d 100644
--- a/Python/coreconfig.c
+++ b/Python/coreconfig.c
@@ -551,6 +551,7 @@ _PyCoreConfig_Init(_PyCoreConfig *config)
     memset(config, 0, sizeof(*config));
 
     config->_config_version = _Py_CONFIG_VERSION;
+    config->_config_init = (int)_PyCoreConfig_INIT;
     config->isolated = -1;
     config->use_environment = -1;
     config->dev_mode = -1;
@@ -612,6 +613,7 @@ _PyCoreConfig_InitPythonConfig(_PyCoreConfig *config)
 {
     _PyCoreConfig_InitDefaults(config);
 
+    config->_config_init = (int)_PyCoreConfig_INIT_PYTHON;
     config->configure_c_stdio = 1;
     config->parse_argv = 1;
 
@@ -624,6 +626,7 @@ _PyCoreConfig_InitIsolatedConfig(_PyCoreConfig *config)
 {
     _PyCoreConfig_InitDefaults(config);
 
+    config->_config_init = (int)_PyCoreConfig_INIT_ISOLATED;
     config->isolated = 1;
     config->use_environment = 0;
     config->user_site_directory = 0;
@@ -643,8 +646,14 @@ _PyCoreConfig_InitIsolatedConfig(_PyCoreConfig *config)
 
 /* Copy str into *config_str (duplicate the string) */
 _PyInitError
-_PyCoreConfig_SetString(wchar_t **config_str, const wchar_t *str)
+_PyCoreConfig_SetString(_PyCoreConfig *config, wchar_t **config_str,
+                        const wchar_t *str)
 {
+    _PyInitError err = _Py_PreInitializeFromCoreConfig(config, NULL);
+    if (_Py_INIT_FAILED(err)) {
+        return err;
+    }
+
     wchar_t *str2;
     if (str != NULL) {
         str2 = _PyMem_RawWcsdup(str);
@@ -662,10 +671,10 @@ _PyCoreConfig_SetString(wchar_t **config_str, const wchar_t *str)
 
 
 static _PyInitError
-_PyCoreConfig_DecodeLocaleErr(wchar_t **config_str, const char *str,
-                              const char *decode_err_msg)
+_PyCoreConfig_DecodeLocaleErr(_PyCoreConfig *config, wchar_t **config_str,
+                              const char *str, const char *decode_err_msg)
 {
-    _PyInitError err = _Py_PreInitialize(NULL);
+    _PyInitError err = _Py_PreInitializeFromCoreConfig(config, NULL);
     if (_Py_INIT_FAILED(err)) {
         return err;
     }
@@ -692,17 +701,18 @@ _PyCoreConfig_DecodeLocaleErr(wchar_t **config_str, const char *str,
 }
 
 
-#define CONFIG_DECODE_LOCALE(config_str, str, NAME) \
-    _PyCoreConfig_DecodeLocaleErr(config_str, str, "cannot decode " NAME)
+#define CONFIG_DECODE_LOCALE(config, config_str, str, NAME) \
+    _PyCoreConfig_DecodeLocaleErr(config, config_str, str, "cannot decode " NAME)
 
 
 /* Decode str using Py_DecodeLocale() and set the result into *config_str.
    Pre-initialize Python if needed to ensure that encodings are properly
    configured. */
 _PyInitError
-_PyCoreConfig_DecodeLocale(wchar_t **config_str, const char *str)
+_PyCoreConfig_DecodeLocale(_PyCoreConfig *config, wchar_t **config_str,
+                           const char *str)
 {
-    return CONFIG_DECODE_LOCALE(config_str, str, "string");
+    return CONFIG_DECODE_LOCALE(config, config_str, str, "string");
 }
 
 
@@ -715,7 +725,7 @@ _PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
 #define COPY_ATTR(ATTR) config->ATTR = config2->ATTR
 #define COPY_WSTR_ATTR(ATTR) \
     do { \
-        err = _PyCoreConfig_SetString(&config->ATTR, config2->ATTR); \
+        err = _PyCoreConfig_SetString(config, &config->ATTR, config2->ATTR); \
         if (_Py_INIT_FAILED(err)) { \
             return err; \
         } \
@@ -727,6 +737,7 @@ _PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
         } \
     } while (0)
 
+    COPY_ATTR(_config_init);
     COPY_ATTR(isolated);
     COPY_ATTR(use_environment);
     COPY_ATTR(dev_mode);
@@ -829,6 +840,7 @@ _PyCoreConfig_AsDict(const _PyCoreConfig *config)
 #define SET_ITEM_WSTRLIST(LIST) \
     SET_ITEM(#LIST, _PyWstrList_AsList(&config->LIST))
 
+    SET_ITEM_INT(_config_init);
     SET_ITEM_INT(isolated);
     SET_ITEM_INT(use_environment);
     SET_ITEM_INT(dev_mode);
@@ -910,7 +922,7 @@ _PyCoreConfig_GetEnv(const _PyCoreConfig *config, const char *name)
    Return 0 on success, but *dest can be NULL.
    Return -1 on memory allocation failure. Return -2 on decoding error. */
 static _PyInitError
-_PyCoreConfig_GetEnvDup(const _PyCoreConfig *config,
+_PyCoreConfig_GetEnvDup(_PyCoreConfig *config,
                         wchar_t **dest,
                         wchar_t *wname, char *name,
                         const char *decode_err_msg)
@@ -930,7 +942,7 @@ _PyCoreConfig_GetEnvDup(const _PyCoreConfig *config,
         return _Py_INIT_OK();
     }
 
-    return _PyCoreConfig_SetString(dest, var);
+    return _PyCoreConfig_SetString(config, dest, var);
 #else
     const char *var = getenv(name);
     if (!var || var[0] == '\0') {
@@ -938,7 +950,7 @@ _PyCoreConfig_GetEnvDup(const _PyCoreConfig *config,
         return _Py_INIT_OK();
     }
 
-    return _PyCoreConfig_DecodeLocaleErr(dest, var, decode_err_msg);
+    return _PyCoreConfig_DecodeLocaleErr(config, dest, var, decode_err_msg);
 #endif
 }
 
@@ -1053,7 +1065,7 @@ config_init_program_name(_PyCoreConfig *config)
        script. */
     const char *p = _PyCoreConfig_GetEnv(config, "PYTHONEXECUTABLE");
     if (p != NULL) {
-        err = CONFIG_DECODE_LOCALE(&config->program_name, p,
+        err = CONFIG_DECODE_LOCALE(config, &config->program_name, p,
                                    "PYTHONEXECUTABLE environment variable");
         if (_Py_INIT_FAILED(err)) {
             return err;
@@ -1067,7 +1079,8 @@ config_init_program_name(_PyCoreConfig *config)
             /* Used by Mac/Tools/pythonw.c to forward
              * the argv0 of the stub executable
              */
-            err = CONFIG_DECODE_LOCALE(&config->program_name, pyvenv_launcher,
+            err = CONFIG_DECODE_LOCALE(config,
+                                       &config->program_name, pyvenv_launcher,
                                        "__PYVENV_LAUNCHER__ environment variable");
             if (_Py_INIT_FAILED(err)) {
                 return err;
@@ -1094,7 +1107,8 @@ config_init_program_name(_PyCoreConfig *config)
 #else
     const wchar_t *default_program_name = L"python3";
 #endif
-    err = _PyCoreConfig_SetString(&config->program_name, default_program_name);
+    err = _PyCoreConfig_SetString(config, &config->program_name,
+                                  default_program_name);
     if (_Py_INIT_FAILED(err)) {
         return err;
     }
@@ -1109,7 +1123,8 @@ config_init_executable(_PyCoreConfig *config)
     /* If Py_SetProgramFullPath() was called, use its value */
     const wchar_t *program_full_path = _Py_path_config.program_full_path;
     if (program_full_path != NULL) {
-        _PyInitError err = _PyCoreConfig_SetString(&config->executable,
+        _PyInitError err = _PyCoreConfig_SetString(config,
+                                                   &config->executable,
                                                    program_full_path);
         if (_Py_INIT_FAILED(err)) {
             return err;
@@ -1135,7 +1150,7 @@ config_init_home(_PyCoreConfig *config)
     /* If Py_SetPythonHome() was called, use its value */
     wchar_t *home = _Py_path_config.home;
     if (home) {
-        _PyInitError err = _PyCoreConfig_SetString(&config->home, home);
+        _PyInitError err = _PyCoreConfig_SetString(config, &config->home, home);
         if (_Py_INIT_FAILED(err)) {
             return err;
         }
@@ -1392,14 +1407,14 @@ config_get_stdio_errors(const _PyCoreConfig *config)
 
 
 static _PyInitError
-config_get_locale_encoding(wchar_t **locale_encoding)
+config_get_locale_encoding(_PyCoreConfig *config, wchar_t **locale_encoding)
 {
 #ifdef MS_WINDOWS
     char encoding[20];
     PyOS_snprintf(encoding, sizeof(encoding), "cp%u", GetACP());
-    return _PyCoreConfig_DecodeLocale(locale_encoding, encoding);
+    return _PyCoreConfig_DecodeLocale(config, locale_encoding, encoding);
 #elif defined(_Py_FORCE_UTF8_LOCALE)
-    return _PyCoreConfig_SetString(locale_encoding, L"utf-8");
+    return _PyCoreConfig_SetString(config, locale_encoding, L"utf-8");
 #else
     const char *encoding = nl_langinfo(CODESET);
     if (!encoding || encoding[0] == '\0') {
@@ -1407,7 +1422,8 @@ config_get_locale_encoding(wchar_t **locale_encoding)
                             "nl_langinfo(CODESET) failed");
     }
     /* nl_langinfo(CODESET) is decoded by Py_DecodeLocale() */
-    return CONFIG_DECODE_LOCALE(locale_encoding, encoding,
+    return CONFIG_DECODE_LOCALE(config,
+                                locale_encoding, encoding,
                                 "nl_langinfo(CODESET)");
 #endif
 }
@@ -1422,7 +1438,7 @@ config_init_stdio_encoding(_PyCoreConfig *config,
     /* If Py_SetStandardStreamEncoding() have been called, use these
         parameters. */
     if (config->stdio_encoding == NULL && _Py_StandardStreamEncoding != NULL) {
-        err = CONFIG_DECODE_LOCALE(&config->stdio_encoding,
+        err = CONFIG_DECODE_LOCALE(config, &config->stdio_encoding,
                                    _Py_StandardStreamEncoding,
                                    "_Py_StandardStreamEncoding");
         if (_Py_INIT_FAILED(err)) {
@@ -1431,7 +1447,7 @@ config_init_stdio_encoding(_PyCoreConfig *config,
     }
 
     if (config->stdio_errors == NULL && _Py_StandardStreamErrors != NULL) {
-        err = CONFIG_DECODE_LOCALE(&config->stdio_errors,
+        err = CONFIG_DECODE_LOCALE(config, &config->stdio_errors,
                                    _Py_StandardStreamErrors,
                                    "_Py_StandardStreamErrors");
         if (_Py_INIT_FAILED(err)) {
@@ -1463,7 +1479,7 @@ config_init_stdio_encoding(_PyCoreConfig *config,
         /* Does PYTHONIOENCODING contain an encoding? */
         if (pythonioencoding[0]) {
             if (config->stdio_encoding == NULL) {
-                err = CONFIG_DECODE_LOCALE(&config->stdio_encoding,
+                err = CONFIG_DECODE_LOCALE(config, &config->stdio_encoding,
                                            pythonioencoding,
                                            "PYTHONIOENCODING environment variable");
                 if (_Py_INIT_FAILED(err)) {
@@ -1482,7 +1498,7 @@ config_init_stdio_encoding(_PyCoreConfig *config,
         }
 
         if (config->stdio_errors == NULL && errors != NULL) {
-            err = CONFIG_DECODE_LOCALE(&config->stdio_errors,
+            err = CONFIG_DECODE_LOCALE(config, &config->stdio_errors,
                                        errors,
                                        "PYTHONIOENCODING environment variable");
             if (_Py_INIT_FAILED(err)) {
@@ -1497,13 +1513,13 @@ config_init_stdio_encoding(_PyCoreConfig *config,
     /* UTF-8 Mode uses UTF-8/surrogateescape */
     if (preconfig->utf8_mode) {
         if (config->stdio_encoding == NULL) {
-            err = _PyCoreConfig_SetString(&config->stdio_encoding, L"utf-8");
+            err = _PyCoreConfig_SetString(config, &config->stdio_encoding, L"utf-8");
             if (_Py_INIT_FAILED(err)) {
                 return err;
             }
         }
         if (config->stdio_errors == NULL) {
-            err = _PyCoreConfig_SetString(&config->stdio_errors,
+            err = _PyCoreConfig_SetString(config, &config->stdio_errors,
                                           L"surrogateescape");
             if (_Py_INIT_FAILED(err)) {
                 return err;
@@ -1513,7 +1529,7 @@ config_init_stdio_encoding(_PyCoreConfig *config,
 
     /* Choose the default error handler based on the current locale. */
     if (config->stdio_encoding == NULL) {
-        err = config_get_locale_encoding(&config->stdio_encoding);
+        err = config_get_locale_encoding(config, &config->stdio_encoding);
         if (_Py_INIT_FAILED(err)) {
             return err;
         }
@@ -1522,7 +1538,7 @@ config_init_stdio_encoding(_PyCoreConfig *config,
         const wchar_t *errors = config_get_stdio_errors(config);
         assert(errors != NULL);
 
-        err = _PyCoreConfig_SetString(&config->stdio_errors, errors);
+        err = _PyCoreConfig_SetString(config, &config->stdio_errors, errors);
         if (_Py_INIT_FAILED(err)) {
             return err;
         }
@@ -1539,34 +1555,35 @@ config_init_fs_encoding(_PyCoreConfig *config, const _PyPreConfig *preconfig)
 
     if (config->filesystem_encoding == NULL) {
 #ifdef _Py_FORCE_UTF8_FS_ENCODING
-        err = _PyCoreConfig_SetString(&config->filesystem_encoding, L"utf-8");
+        err = _PyCoreConfig_SetString(config, &config->filesystem_encoding, L"utf-8");
 #else
 
 #ifdef MS_WINDOWS
         if (preconfig->legacy_windows_fs_encoding) {
             /* Legacy Windows filesystem encoding: mbcs/replace */
-            err = _PyCoreConfig_SetString(&config->filesystem_encoding,
+            err = _PyCoreConfig_SetString(config, &config->filesystem_encoding,
                                           L"mbcs");
         }
         else
 #endif
         if (preconfig->utf8_mode) {
-            err = _PyCoreConfig_SetString(&config->filesystem_encoding,
+            err = _PyCoreConfig_SetString(config, &config->filesystem_encoding,
                                           L"utf-8");
         }
 #ifndef MS_WINDOWS
         else if (_Py_GetForceASCII()) {
-            err = _PyCoreConfig_SetString(&config->filesystem_encoding,
+            err = _PyCoreConfig_SetString(config, &config->filesystem_encoding,
                                           L"ascii");
         }
 #endif
         else {
 #ifdef MS_WINDOWS
             /* Windows defaults to utf-8/surrogatepass (PEP 529). */
-            err = _PyCoreConfig_SetString(&config->filesystem_encoding,
+            err = _PyCoreConfig_SetString(config, &config->filesystem_encoding,
                                           L"utf-8");
 #else
-            err = config_get_locale_encoding(&config->filesystem_encoding);
+            err = config_get_locale_encoding(config,
+                                             &config->filesystem_encoding);
 #endif
         }
 #endif   /* !_Py_FORCE_UTF8_FS_ENCODING */
@@ -1588,7 +1605,7 @@ config_init_fs_encoding(_PyCoreConfig *config, const _PyPreConfig *preconfig)
 #else
         errors = L"surrogateescape";
 #endif
-        err = _PyCoreConfig_SetString(&config->filesystem_errors, errors);
+        err = _PyCoreConfig_SetString(config, &config->filesystem_errors, errors);
         if (_Py_INIT_FAILED(err)) {
             return err;
         }
@@ -1681,7 +1698,7 @@ config_read(_PyCoreConfig *config)
     }
 
     if (config->check_hash_pycs_mode == NULL) {
-        err = _PyCoreConfig_SetString(&config->check_hash_pycs_mode,
+        err = _PyCoreConfig_SetString(config, &config->check_hash_pycs_mode,
                                       L"default");
         if (_Py_INIT_FAILED(err)) {
             return err;
@@ -1832,7 +1849,7 @@ config_parse_cmdline(_PyCoreConfig *config, _PyWstrList *warnoptions,
                 || wcscmp(_PyOS_optarg, L"never") == 0
                 || wcscmp(_PyOS_optarg, L"default") == 0)
             {
-                err = _PyCoreConfig_SetString(&config->check_hash_pycs_mode,
+                err = _PyCoreConfig_SetString(config, &config->check_hash_pycs_mode,
                                               _PyOS_optarg);
                 if (_Py_INIT_FAILED(err)) {
                     return err;
@@ -1966,7 +1983,7 @@ config_parse_cmdline(_PyCoreConfig *config, _PyWstrList *warnoptions,
 
 /* Get warning options from PYTHONWARNINGS environment variable. */
 static _PyInitError
-config_init_env_warnoptions(const _PyCoreConfig *config, _PyWstrList *warnoptions)
+config_init_env_warnoptions(_PyCoreConfig *config, _PyWstrList *warnoptions)
 {
     _PyInitError err;
     /* CONFIG_GET_ENV_DUP requires dest to be initialized to NULL */
@@ -2136,8 +2153,7 @@ core_read_precmdline(_PyCoreConfig *config, _PyPreCmdline *precmdline)
     }
 
     _PyPreConfig preconfig;
-    _PyPreConfig_Init(&preconfig);
-    _PyPreConfig_Copy(&preconfig, &_PyRuntime.preconfig);
+    _PyPreConfig_InitFromPreConfig(&preconfig, &_PyRuntime.preconfig);
 
     _PyPreConfig_GetCoreConfig(&preconfig, config);
 
@@ -2211,24 +2227,11 @@ done:
 _PyInitError
 _PyCoreConfig_SetPyArgv(_PyCoreConfig *config, const _PyArgv *args)
 {
-    if (args->use_bytes_argv) {
-        _PyInitError err;
-
-        err = _PyRuntime_Initialize();
-        if (_Py_INIT_FAILED(err)) {
-            return err;
-        }
-        _PyRuntimeState *runtime = &_PyRuntime;
-
-        /* do nothing if Python is already pre-initialized:
-           _PyCoreConfig_Write() will update _PyRuntime.preconfig later */
-        if (!runtime->pre_initialized) {
-            err = _Py_PreInitializeFromCoreConfig(config, args);
-            if (_Py_INIT_FAILED(err)) {
-                return err;
-            }
-        }
+    _PyInitError err = _Py_PreInitializeFromCoreConfig(config, args);
+    if (_Py_INIT_FAILED(err)) {
+        return err;
     }
+
     return _PyArgv_AsWstrList(args, &config->argv);
 }
 
@@ -2236,7 +2239,7 @@ _PyCoreConfig_SetPyArgv(_PyCoreConfig *config, const _PyArgv *args)
 /* Set config.argv: decode argv using Py_DecodeLocale(). Pre-initialize Python
    if needed to ensure that encodings are properly configured. */
 _PyInitError
-_PyCoreConfig_SetArgv(_PyCoreConfig *config, Py_ssize_t argc, char **argv)
+_PyCoreConfig_SetArgv(_PyCoreConfig *config, Py_ssize_t argc, char * const *argv)
 {
     _PyArgv args = {
         .argc = argc,
@@ -2248,7 +2251,7 @@ _PyCoreConfig_SetArgv(_PyCoreConfig *config, Py_ssize_t argc, char **argv)
 
 
 _PyInitError
-_PyCoreConfig_SetWideArgv(_PyCoreConfig *config, Py_ssize_t argc, wchar_t **argv)
+_PyCoreConfig_SetWideArgv(_PyCoreConfig *config, Py_ssize_t argc, wchar_t * const *argv)
 {
     _PyArgv args = {
         .argc = argc,
diff --git a/Python/preconfig.c b/Python/preconfig.c
index 0f4bd8ece53..71a6ee6c072 100644
--- a/Python/preconfig.c
+++ b/Python/preconfig.c
@@ -95,7 +95,7 @@ _PyArgv_AsWstrList(const _PyArgv *args, _PyWstrList *list)
     }
     else {
         wargv.length = args->argc;
-        wargv.items = args->wchar_argv;
+        wargv.items = (wchar_t **)args->wchar_argv;
         if (_PyWstrList_Copy(list, &wargv) < 0) {
             return _Py_INIT_NO_MEMORY();
         }
@@ -217,16 +217,15 @@ precmdline_parse_cmdline(_PyPreCmdline *cmdline)
 
 
 _PyInitError
-_PyPreCmdline_Read(_PyPreCmdline *cmdline,
-                    const _PyPreConfig *preconfig)
+_PyPreCmdline_Read(_PyPreCmdline *cmdline, const _PyPreConfig *preconfig)
 {
-    if (preconfig) {
-        _PyPreCmdline_GetPreConfig(cmdline, preconfig);
-    }
+    _PyPreCmdline_GetPreConfig(cmdline, preconfig);
 
-    _PyInitError err = precmdline_parse_cmdline(cmdline);
-    if (_Py_INIT_FAILED(err)) {
-        return err;
+    if (preconfig->parse_argv) {
+        _PyInitError err = precmdline_parse_cmdline(cmdline);
+        if (_Py_INIT_FAILED(err)) {
+            return err;
+        }
     }
 
     /* isolated, use_environment */
@@ -268,6 +267,7 @@ _PyPreConfig_Init(_PyPreConfig *config)
     memset(config, 0, sizeof(*config));
 
     config->_config_version = _Py_CONFIG_VERSION;
+    config->parse_argv = 0;
     config->isolated = -1;
     config->use_environment = -1;
     config->configure_locale = 1;
@@ -285,6 +285,7 @@ _PyPreConfig_InitPythonConfig(_PyPreConfig *config)
 {
     _PyPreConfig_Init(config);
 
+    config->parse_argv = 1;
     /* Set to -1 to enable C locale coercion (PEP 538) and UTF-8 Mode (PEP 540)
        depending on the LC_CTYPE locale, PYTHONUTF8 and PYTHONCOERCECLOCALE
        environment variables. */
@@ -310,11 +311,41 @@ _PyPreConfig_InitIsolatedConfig(_PyPreConfig *config)
 }
 
 
+void
+_PyPreConfig_InitFromPreConfig(_PyPreConfig *config,
+                               const _PyPreConfig *config2)
+{
+    _PyPreConfig_Init(config);
+    _PyPreConfig_Copy(config, config2);
+}
+
+
+void
+_PyPreConfig_InitFromCoreConfig(_PyPreConfig *config,
+                                const _PyCoreConfig *coreconfig)
+{
+    _PyCoreConfigInitEnum config_init = (_PyCoreConfigInitEnum)coreconfig->_config_init;
+    switch (config_init) {
+    case _PyCoreConfig_INIT_PYTHON:
+        _PyPreConfig_InitPythonConfig(config);
+        break;
+    case _PyCoreConfig_INIT_ISOLATED:
+        _PyPreConfig_InitIsolatedConfig(config);
+        break;
+    case _PyCoreConfig_INIT:
+    default:
+        _PyPreConfig_Init(config);
+    }
+    _PyPreConfig_GetCoreConfig(config, coreconfig);
+}
+
+
 void
 _PyPreConfig_Copy(_PyPreConfig *config, const _PyPreConfig *config2)
 {
 #define COPY_ATTR(ATTR) config->ATTR = config2->ATTR
 
+    COPY_ATTR(parse_argv);
     COPY_ATTR(isolated);
     COPY_ATTR(use_environment);
     COPY_ATTR(configure_locale);
@@ -341,27 +372,20 @@ _PyPreConfig_AsDict(const _PyPreConfig *config)
         return NULL;
     }
 
-#define SET_ITEM(KEY, EXPR) \
+#define SET_ITEM_INT(ATTR) \
         do { \
-            PyObject *obj = (EXPR); \
+            PyObject *obj = PyLong_FromLong(config->ATTR); \
             if (obj == NULL) { \
                 goto fail; \
             } \
-            int res = PyDict_SetItemString(dict, (KEY), obj); \
+            int res = PyDict_SetItemString(dict, #ATTR, obj); \
             Py_DECREF(obj); \
             if (res < 0) { \
                 goto fail; \
             } \
         } while (0)
-#define SET_ITEM_INT(ATTR) \
-    SET_ITEM(#ATTR, PyLong_FromLong(config->ATTR))
-#define FROM_STRING(STR) \
-    ((STR != NULL) ? \
-        PyUnicode_FromString(STR) \
-        : (Py_INCREF(Py_None), Py_None))
-#define SET_ITEM_STR(ATTR) \
-    SET_ITEM(#ATTR, FROM_STRING(config->ATTR))
 
+    SET_ITEM_INT(parse_argv);
     SET_ITEM_INT(isolated);
     SET_ITEM_INT(use_environment);
     SET_ITEM_INT(configure_locale);
@@ -379,10 +403,7 @@ fail:
     Py_DECREF(dict);
     return NULL;
 
-#undef FROM_STRING
-#undef SET_ITEM
 #undef SET_ITEM_INT
-#undef SET_ITEM_STR
 }
 
 
@@ -395,6 +416,7 @@ _PyPreConfig_GetCoreConfig(_PyPreConfig *config,
         config->ATTR = core_config->ATTR; \
     }
 
+    COPY_ATTR(parse_argv);
     COPY_ATTR(isolated);
     COPY_ATTR(use_environment);
     COPY_ATTR(dev_mode);
@@ -662,9 +684,11 @@ preconfig_init_allocator(_PyPreConfig *config)
            allocators to "malloc" (and not to "debug"). */
         const char *envvar = _Py_GetEnv(config->use_environment, "PYTHONMALLOC");
         if (envvar) {
-            if (_PyMem_GetAllocatorName(envvar, &config->allocator) < 0) {
+            PyMemAllocatorName name;
+            if (_PyMem_GetAllocatorName(envvar, &name) < 0) {
                 return _Py_INIT_ERR("PYTHONMALLOC: unknown allocator");
             }
+            config->allocator = (int)name;
         }
     }
 
@@ -751,8 +775,7 @@ _PyPreConfig_Read(_PyPreConfig *config, const _PyArgv *args)
 
     /* Save the config to be able to restore it if encodings change */
     _PyPreConfig save_config;
-    _PyPreConfig_Init(&save_config);
-    _PyPreConfig_Copy(&save_config, config);
+    _PyPreConfig_InitFromPreConfig(&save_config, config);
 
     /* Set LC_CTYPE to the user preferred locale */
     if (config->configure_locale) {
@@ -879,8 +902,9 @@ _PyPreConfig_Write(const _PyPreConfig *config)
         return _Py_INIT_OK();
     }
 
-    if (config->allocator != PYMEM_ALLOCATOR_NOT_SET) {
-        if (_PyMem_SetupAllocators(config->allocator) < 0) {
+    PyMemAllocatorName name = (PyMemAllocatorName)config->allocator;
+    if (name != PYMEM_ALLOCATOR_NOT_SET) {
+        if (_PyMem_SetupAllocators(name) < 0) {
             return _Py_INIT_ERR("Unknown PYTHONMALLOC allocator");
         }
     }
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 0781dc8046b..01f725f8f45 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -691,6 +691,10 @@ _Py_PreInitializeFromPyArgv(const _PyPreConfig *src_config, const _PyArgv *args)
 {
     _PyInitError err;
 
+    if (src_config == NULL) {
+        return _Py_INIT_ERR("preinitialization config is NULL");
+    }
+
     err = _PyRuntime_Initialize();
     if (_Py_INIT_FAILED(err)) {
         return err;
@@ -703,11 +707,7 @@ _Py_PreInitializeFromPyArgv(const _PyPreConfig *src_config, const _PyArgv *args)
     }
 
     _PyPreConfig config;
-    _PyPreConfig_Init(&config);
-
-    if (src_config) {
-        _PyPreConfig_Copy(&config, src_config);
-    }
+    _PyPreConfig_InitFromPreConfig(&config, src_config);
 
     err = _PyPreConfig_Read(&config, args);
     if (_Py_INIT_FAILED(err)) {
@@ -751,21 +751,34 @@ _PyInitError
 _Py_PreInitializeFromCoreConfig(const _PyCoreConfig *coreconfig,
                                 const _PyArgv *args)
 {
-    _PyPreConfig config;
-    _PyPreConfig_Init(&config);
-    if (coreconfig != NULL) {
-        _PyPreConfig_GetCoreConfig(&config, coreconfig);
+    assert(coreconfig != NULL);
+
+    _PyInitError err = _PyRuntime_Initialize();
+    if (_Py_INIT_FAILED(err)) {
+        return err;
+    }
+    _PyRuntimeState *runtime = &_PyRuntime;
+
+    if (runtime->pre_initialized) {
+        /* Already initialized: do nothing */
+        return _Py_INIT_OK();
     }
 
-    if (args == NULL && coreconfig != NULL && coreconfig->parse_argv) {
+    _PyPreConfig preconfig;
+    _PyPreConfig_InitFromCoreConfig(&preconfig, coreconfig);
+
+    if (!coreconfig->parse_argv) {
+        return _Py_PreInitialize(&preconfig);
+    }
+    else if (args == NULL) {
         _PyArgv config_args = {
             .use_bytes_argv = 0,
             .argc = coreconfig->argv.length,
             .wchar_argv = coreconfig->argv.items};
-        return _Py_PreInitializeFromPyArgv(&config, &config_args);
+        return _Py_PreInitializeFromPyArgv(&preconfig, &config_args);
     }
     else {
-        return _Py_PreInitializeFromPyArgv(&config, args);
+        return _Py_PreInitializeFromPyArgv(&preconfig, args);
     }
 }
 
@@ -777,13 +790,11 @@ pyinit_coreconfig(_PyRuntimeState *runtime,
                   const _PyArgv *args,
                   PyInterpreterState **interp_p)
 {
-    _PyInitError err;
+    assert(src_config != NULL);
 
-    if (src_config) {
-        err = _PyCoreConfig_Copy(config, src_config);
-        if (_Py_INIT_FAILED(err)) {
-            return err;
-        }
+    _PyInitError err = _PyCoreConfig_Copy(config, src_config);
+    if (_Py_INIT_FAILED(err)) {
+        return err;
     }
 
     if (args) {
@@ -995,6 +1006,10 @@ _Py_InitializeMain(void)
 static _PyInitError
 init_python(const _PyCoreConfig *config, const _PyArgv *args)
 {
+    if (config == NULL) {
+        return _Py_INIT_ERR("initialization config is NULL");
+    }
+
     _PyInitError err;
 
     err = _PyRuntime_Initialize();
@@ -1022,7 +1037,8 @@ init_python(const _PyCoreConfig *config, const _PyArgv *args)
 
 
 _PyInitError
-_Py_InitializeFromArgs(const _PyCoreConfig *config, Py_ssize_t argc, char **argv)
+_Py_InitializeFromArgs(const _PyCoreConfig *config,
+                       Py_ssize_t argc, char * const *argv)
 {
     _PyArgv args = {.use_bytes_argv = 1, .argc = argc, .bytes_argv = argv};
     return init_python(config, &args);
@@ -1030,7 +1046,8 @@ _Py_InitializeFromArgs(const _PyCoreConfig *config, Py_ssize_t argc, char **argv
 
 
 _PyInitError
-_Py_InitializeFromWideArgs(const _PyCoreConfig *config, Py_ssize_t argc, wchar_t **argv)
+_Py_InitializeFromWideArgs(const _PyCoreConfig *config,
+                           Py_ssize_t argc, wchar_t * const *argv)
 {
     _PyArgv args = {.use_bytes_argv = 0, .argc = argc, .wchar_argv = argv};
     return init_python(config, &args);